Current tap changing system



June 22, 1954 B. JANSEN 2,682,030

CURRENT TAP CHANGING SYSTEM FIG. BgRNhqYd TANSEN @u Affomev /nvenhor June 22, 1954 B. JANSEN 2,682,030 CURRENT TAP CHANGING SYSTEM Filed March '7, 1951 5 Sheets-SheeiI 2 BsnNHnRo TNWE N R. 2 ,ym QWQWN June 22, 1954 B JANSEN 2,682,030

CURRENT TAP CHANGING SYSTEM Filed March 7, 1951 5 Sheets-Sheet 3 BERNHARD :YAN

by .9 :l fpm@ @My-IM division :of thelcadf -ever,fprovldesi-for La three-wayiloaddivision;

Patented June 22V, 1954 ortica V2;fss2,o:-it y CURRENTTAP cnAnlInGfsYs'rEM u BernhardJansen, Regali-sinirg,"Germany .Aiipi'iciin 195i, seal No@ 214,279

l y The present inventionf relates to transfer switches for operationunderiload, andv more particularly to switches ofv this character which are suitable for use in changing transformer "taps under load. .t v,

-Anoknectiof they invention is to provide atransfer switch of this character rin `which the load current vis divided among three separate pairs of contactsjso arranged that the load current will be equally distributed to minimize arcing 'and the accompanying burningof the contacts.

A-eature of Nthe inventionresides inthe .provisionof inductively coupled current dividing circuit elements which Vact -to equalize the, distribution of the load current; vparticularly-"duri'ng transient conditions 'when contact arcing, is 'taliing place.` Theinductive"couplingisl so arranged `that,^`during initialcontact opening under load,

if the'V arc Vat 4one of 4the contacts `should become extinguished; the-accompanying increase 'in current Liiowy thmgiugh;v the other contacts vwillinducje aI voltage sufficient to restrike :the arc and 'redis- Atri-laute Athe arcing vfsubstantiallyv equally among the contacts.r techniquehasfpreviouslybeen applied to Y mercury vapor'rrectiers fora 'two-way The present invention-,"how

The present invention permits `the `operation o Sthreefpairs-of equally rated-contactsto `obtain a=current rating fforthe groupyo'f three times 'the 1individual rating of each contact pair andavoids vthe necessity -for precise mechanical adjustments to Iobtain equal current distribution f and distribuf ftionfrof aijcing among V the three contact` ,airs.

@ther G biecte and advantages .will become .an-

parent upon' reading jthe v,following specicatiofn ltogether with the accompanyingrdrawlingstorming a part hereof. v

IReferring tojthe drawing;v n Y Y c Figura 1 a schematic circuit .diagramiillustrating-ancrnbodiment of'jthe' 'inventionllas lapplied to a transformertap preselector and changeover switch for changing transformer taps. under load, the inductively coupled loadl-equalizing circuitwelements being connected :between the `tap preselectorA and the changeover switch. i.

Figure 1,2 is similar to Fi'g.1,except that the 'changeover lswitch is .Y provided Vwith ,additional contacts which normally short circuit the inductively coupled circuit-elements and introduce them in the circuit only momentarily during the short interval of operation of the changeover switch.

Figure 3 is similar to Fig. 1, except that the inductive circuit elements are associated with -ual magnetic icore; drawing indicate the Vm'atu'relyA extinguished [lojad changeoversw-itch arms yLi--to Laftowardthe left `from-the positionfshown in dotted lines to- "ward the position .shown in solidlines, .as indithe 'line conductor'leading to the changeover switch; Y :Fig: v1 shows `a'transformer tap changing regula-ting switch with 4three-way currentv division betweenthe'l tapprese1ector and the load change'- overswitch by permanently lconnected current equalizers with*separate-magnetic cores (left) and with a common-core (right). The'tappreselector Vrepresented in the lower part of the drawing bythe 6 tapcontact surfaces Wai to `Was and Wbl to Wiss and by the -6 'mov-able' contacts a1 tous and rZn to -bwhich are connected-to the two transformer tapsyAand B; This three-'way division is'continuedA after vpassing through the current equalizingv windings and -in `the load changeover switch Har to I-Iaa andV I-Ibi to Hb:

through the three-'switch arms L1 to L3, the three vswitch-arms L1 to La beingshown connectedto a `Acommcnline'conductor-A1;-

4'Equalization of the current division isv eiected,

as shown on the left side, `bythe inductivel'y coupled windin'gs an and alzwhich having la commonlmagnet core inductively coupled windings oppose each other, Stai. Similarly the azi and `G22 areplo- -vided with a commoncore'staz and the windings aar and u32 are coupled 4by a common magnetic core St'vtaeachv of the' three pairs 'of inductively coupledwi-ndingsbeing provided with an individ- 'The arrows shown inthe direction of` the magnetic fluir generated by each individual winding. If

the-individual' winding currents are equal, these "arc drawn at changeoveriswitch contactseI-Ibi and hin 'by ,inte1-r uption.-of..current owing `through .tanpr'eselector switch contact bicis preduring movementof the cated .,bycthe arrows yThe current 1in each,v of the other .two .-,branches baandlas .suddenly inof the` total;Y current to :a lvalue fo'f 1,/2A tolftheitotal current r The i'lux produced' in-the middle core ,legistbalanced `out;x The `magnetiza- .tionin the ,two-:outealegs .fissuchfas'atacause flux to flow around the core structure as indicated by the arrows. The relative polarities of the windings are so arranged that the load carrying wlndngs blz and bai induce cumulative voltages in the series connected windings 1932 and bi1, current now through windings B32 and bn having been interrupted by the assumed premature extinguishing of the arc at changeover switch arm L1. The direction of these induced voltages is such as to raise the voltage at stationary contacts Hin and hln, thereby tendingto restrike the prematurely extinguished arc and equalize the arcing at the three switch arms L1 to La of the changeover switch. By suitably dimensioning the two electromagnetic structures each comprising three pairs of inductively coupled coils, the magnitude of the induced voltage accompanying a premature decrease in current in any of the three circuit branches may be made sufficient to restore the prematurely decreasing current to its proper value, restriking an arc, if necessary.

Fig. 2 shows a regulating switch with threeway current division between the tap preselec- `tor and the load changeover switch, the inductively coupled circuit elements being effective only momentarily during the relatively short interval of switching operation of the load changeover switch. The current equalizing circuit elements are normally short-circuited through the stationary main contacts and stationary switch- `ing Han-DH1, Haz- Daz and Has-Dae which are bridged by the switch arms L1, L2 and La, respectively, in one of the two normal positions of the changeover switch as shown in Fig. 2 of the drawing. The stationary contacts Hb1-Db1, Hbz--Dbz and Hba-Dbz are similarly bridged by the switch arms L1, L2 and L3, respectively, when the changeover switch is operated to its other normal position by moving the switch arms L1 to Lc to the right, or in a clockwise direction as viewed in Fig. 2, thereby short circuiting the inductively coupled circuit elements shown on the right hand side of Fig. 2 which are coupled by a common Aunitary magnetic core structure.

The divided current loads from the preselected transformer tap leads A and B flow through either of the two groups of main stationary contacts Da1 to Das or Db1 to Dba, respectively in each of the two positions of the changeover switch. As in Fig. 1, the currents from the three yswitch arms L1 to Le of the changeover switch are combined in the common line conductor A1.

Assuming the changeover switch to be in the position shown in Fig. 2, as the switcharms L1 'to Lc move toward the right, the circuit through the main stationary contacts Da1 'to Das is broken and the three load currents flow through 4the main switching contacts Han to Has, passing through the left hand group of inductively coupled current equalizing circuit elements.

The main stationary contacts Dai to Das are not designed to withstand arcing, and the potential drop across the current equalizing circuit ele- `ments must accordingly be limited to a value suiciently small to prevent appreciable arcing.

As the switch arms L1 to La proceed further toward the right, the circuit is broken and arcing `occurs at the main switching contacts Hm to Has,

the three currents being equalized by the left hand group of inductively coupled circuit elements as this arcing occurs. The iinal current interruption takes place with the current equalizers in the circuit as the three switch arms L1 to L3 disengage the auxiliary switching contacts hai to has which are connected to the respective main switching contacts Ha1 to Has through non-inductive resistors. A similar switching sequence takes place as the switch arms L1 to La are moved back from their right hand position to their original starting position shown in Fig. 2.

Fig. 3 shows a regulating switch with threeway equalized current division, in which the inductively coupled current equalizing circuit elements are connected between the main line conductor A1 and the three switch arms L1 to L3 of the changeover switch. Using this arrangement, only one set of current equalizing circuit elements is required, however, the three switch arms L1 to La must be insulated from each other.

In the arrangements of Fig. 1 and Fig. 3, the current equalizing circuit elements must be designed for continuous duty and must be capable of withstanding the usual current surges on the line. In the arrangement of Fig. 2, the current equalizing circuit elements may be designed for momentary duty and are not required to withstand surge currents, except if a surge should occur during the instant of changeover switch operation.

In the arrangements of Figs. 1 and 3, the current equalizing circuit elements are continuously `effective for the load currents so that the load `contact of each of said contact pairs being connected to one of said conductors; three pairs of inductively coupled circuit elements, each circuit element having two terminals, one terminal of one circuit element of each pair being connected to-the other contact of each of said contact pairs and one terminal of the other circuit element of each pair being connected to the other of said two conductors, the remaining terminal of each yof said circuit elements being connected to the remaining terminal of one of the circuit elements of another pair to complete a circuit from one of said other contacts to said other conductor, the respective polarities of the inductive coupling between each pair of circuit elements being such that a reduction in current flow through one of said contact pairs tending to increase current ow through the other two contact pairs induces a `cumulative voltage in the two circuit elements connected between said contact pair in which said current reduction takes place and said other conductor tending to increase said reduced current flow and prevent said current reduction, whereby equal current distribution in said three pairs of cooperating contacts is maintained.

2. Current equalizing means according to claim l, in which said inductively coupled circuit elements are coupled through a common magnetic core structure.

3. Current equalizing means according to claim l, in which the inductively coupled circuit elements of each pair are coupled through an individual magnetic core structure.

No references cited. 

